"All bishops were asked to alert parishioners of the need to address the threat to religious liberty found in (the) HHS mandate related to health care reform," said Sister Mary Ann Walsh, a spokeswoman for the bishops conference.

Under a new rule developed as part of implementing health care reform, employers will be required to offer employees insurance packages that include a range of preventive health services without co-pays.

Developed by the Institute of Medicine, an arm of the National Academy of Sciences, the list includes services like mammograms, colonoscopies and childhood immunizations.

But more controversially, the rule also requires that insurance plans offer sterilization services and birth control, including
"morning-after" emergency contraceptive methods already approved by the Food and Drug Administration.

While Planned Parenthood and other supporters regard the inclusion of free contraception as a significant victory for women, the Roman Catholic Church regards contraception as illicit because it artificially splits sex from the possibility of procreation.

Many Catholics and evangelicals also regard "day-after" birth control as theoretically indistinguishable from abortion.

Catholic leaders say the church, as an employer, should not have to offer employees coverage for medical practices that the employer finds morally objectionable.

They also say an exemption -- which covers organizations whose purpose is to inculcate religious doctrine and organizations that hire and serve mostly those of their own faith -- is too narrow because it excludes faith-based ministries such as hospitals, battered women's shelters and groups like Catholic Charities that serve all those in need, regardless of faith.

(Bruce Nolan writes for The Times-Picayune in New Orleans. Kevin Eckstrom contributed to this report from Washington.)